Mayo Clinic’s website describes some of the more serious causes of leg cramps. Inadequate blood supply caused by arteriosclerosis, which is a narrowing of arteries delivering blood to the extremities, can be a very painful cause of leg cramps. Another cause is nerve compression, which is a result of pressure on the nerves. Nerve compression within the lumbar region can result in cramping in the legs, according to WebMD. Additionally, depletion of minerals such as potassium and magnesium within the body may cause leg cramps.